Nucleophilic addition reaction of aldehydes and ketones catalyzed by bases is a carbon-carbon bond-generating reaction and is recognized as one of the most important catalytic reactions for organic synthesis of the present day. Heterogeneous reacting systems that use solid catalysts on which basic functional groups such as an amino group are immobilized are advantageous for repeated use since catalysts can be easily separated and recovered from solutions upon completion of the reaction, and are thus extensively studied.
In general, aldehydes and ketones are known to exhibit improved activity to nucleophilic addition reactions due to the decrease in electronic density on oxygen of carbonyl units contained therein by the action of proton acids, Lewis acids, and hydrogen-bonding proton donors. Actually, NPL 1 discloses that silica gel having a surface into which both an amino (base)-containing silane compound and a urea bond (hydrogen bonding proton donor)-containing silane compound are introduced functions as a highly active solid catalyst for nucleophilic addition reactions such as aldol reactions of aldehydes.
A dendrimer (a1) typically exemplified by a poly(amidoamine) dendrimer and a poly(propylene imine) dendrimer and a straight-chain or branched polyethyleneimine (a2) are amino-containing organic polymers and are useful molecules in which plural amino groups can be highly densely incorporated in one molecule. Polymerizable compounds (a) prepared from such a dendrimer (a1) and a polyethyleneimine (a2) have been known; for example, PTL 1 describes an energy-curable compound having a polymerizable vinyl group at a terminus of a molecular chain of a poly(amidoamine) dendrimer or a poly(propylene imine) dendrimer and discloses a technology of using this compound as a material for a film-forming material such as paint and ink, a sealant, a molding agent, an adhesive, a resin for a tackiness agent, a curing agent for a heat/radiation-curable resin composition, or a reactive diluent. PTL 2 discloses examples of using a poly(amidoamine) dendrimer or a poly(propylene imine) dendrimer immobilized on an insoluble carrier as a stabilizing scavenger for generating metal particles. PTL 3 discloses examples of using a hydro gel formed by a polymer having a straight-chain polyethyleneimine skeleton as a carrier for generating metal particles.
However, a technique for forming these compounds into organic polymer porous materials having large specific surface areas and a technique of using the porous materials as base catalysts to be used in nucleophilic addition reactions of aldehydes and ketones have not been disclosed.
Furthermore, chemical reactions using catalysts containing transition metals such as palladium, platinum, ruthenium, rhodium, gold, silver, and rhenium are recognized as the most important catalytic reaction for organic synthesis of the present day, as is representatively shown by carbon-carbon coupling reactions. In reacting systems that use transition metal catalysts, a homogeneous catalyst in which a transition metal catalyst is dissolved in a reaction solution is usually used. However, since transition metal catalysts are generally expensive, they are preferably used repeatedly. Since a catalyst is dissolved in a reaction solution according to a homogeneous catalyst, separation and recovery of the catalyst after reaction is not easy. Accordingly, studies have been made on use of heterogeneous catalysts in which transition metal catalysts are immobilized on insoluble solids.
PTL 4 reports an example of synthesizing a poly(amidoamine) dendrimer (a1) on a surface of silica gel and adsorption and incorporation of a salt of a metal, such as palladium, into the dendrimer. According to this technique, operation for synthesizing the dendrimer is complicated and the metal content in the silica gel is not necessarily high.
PTL 2 described above reports an example of incorporating metal nanoparticles in silica gel by allowing a poly(propylene imine) dendrimer, into which nanoparticles of a metal such as palladium had been introduced in advance, to be present during the course of porous silica gel preparation by a sol-gel reaction. According to this technique, the metal content in the silica gel is not necessarily high since an alkoxysilane compound, i.e., a silica raw material, is used in excess.